51813_Sturgeon biodioversity an.PDF

year in the Connecticut, Hudson, Savannah, and

Altamaha rivers, and in the Saint John River during

summer juveniles use the same fresh water or fresh/

saltwater interface as adults (Dadswell 1979, Hall et

al. 1991, Savoy & Shake^3 , Dovel el al. 1992, Flournoy

et al.^10 , Rogers & Weber^9 ). Juveniles 2-3 year old

and adults occur together in freshwater concentra-

tion areas in the Connecticut River (Taubert 1980a,

M. Kieffer & B. Kynard unpublished data). Juve-

niles 1-year and older and adults in the Connecticut

River had similar summer home ranges (respective

means, 6.3 and 4.9 km) and winter home ranges (re-

spective means, 2.7 and 2.6 km; B. Kynard, D. Sei-

bel, M. Kieffer & M. Horgan unpublished data).

The similarity of home ranges further indicates that

juveniles use space similar to adults.

Concentration areas used by juveniles and adults

in fresh water are often located upstream of natural

constrictions or in headwaters of dammed reaches.

locations where river velocity slows and creates

large sandy shoals (Buckley & Kynard 1985a, Kieff-

er & Kynard 1993). Perhaps. these geomorpholog-

ical features create hydraulic conditions that favor

substrate for freshwater mussels, a major food item

of adults (Dadswelletal. 1984). Adults also feed on

introduced bivalves, including the introduced zebra

mussel, Dressena polymorpha (M. Bain personal

Habitat use of juveniles and adults has been stud-

ied in several rivers. Juveniles in the Saint John,

Hudson, and Savannah rivers use sand and mud

substrate in deep channels (Pottle & Dadswell^15 ,

Hall et al. 1991, Dovel el al. 1992). Some Saint John

River adults foraged during summer in backwaters

of fresh to low salinity lakes with aquatic vegetation

or on mud substrate along river banks (Dadswell

1979). During summer and winter in freshwater

reaches of the Connecticut River, juveniles and

adults selected similar geomorphological reaches of

curves and runs with island, but not straight runs

(Seibel 1993). Juveniles and adults forage in channel

and shoal areas (Dadswell 1979, O’Herron el al.

1993), but Connecticut River juveniles used shoals

more at night than adults (Seibel 1993). Although

use of channel and shoal areas was highly variable

among individuals during summer and fall, all Con-

necticut River juveniles and adults overwintered in

data). This is sufficient time to move many kilome-
ters downstream, but not sufficient time to move to
the estuary from any known unobstructed spawn-
ing location.
Tolerance of early life stages to increasing salinity
and low dissolved oxygen increases with age. Twen-
ty-two day old larvae from the Savannah River tol-
crated a maximum of 9 ppt salinity and required
more than 3 mg l–1oxygen, while fish about 300 days
old tolerated 25 ppt salinity for 18 hours and most
survived short periods of 3 mg 1–1oxygen (Jenkins et
al. 1993).

Young-of-the-year

Behavior and movements of young-of-the-year

(YOY) are not fully understood in any river, but da-

ta from rivers throughout the range suggest that fish

remain upriver in fresh water for about 1 year. In the

Saint John River, YOY and older juveniles remain

in fresh water, growing slowly for several years

(Dadswell 1979). Some Hudson River YOY occur

within 18 km of Troy Dam, the upstream limit of

spawning. They apparently remain in fresh water

for about 1 year before moving downstream to the

fresh/saltwater interface (Carlson & Simpson 1987,

Dovel et al. 1992). communication).

Sparse information is available on feeding and

habitat use of YOY. Carlson & Simpson (1987)

found YOY foraged in channel habitat on amphi-

pods and dipteran larvae on mud not sand sub-

strate. Saint John River YOY used deep water and

intermediate depth areas (Pottle & Dadswell).^15

One-year old juveiles and adults

With the exception of the Saint John River, where

all juveniles remain in fresh water for several years

(Dadswell et al. 1984), l-year old and older juveniles

in other populations join adults and show similar

spatio-temporal patterns of habitat use. During all

(^15) Pottle, R. & M. J. Dadswell. 1979. Studies on larval and juvenile
shortnose sturgeon (Acipenser brevirostrum). Report toNorth
east Utilities Service Co., Hartford. 79 pp.